Esketamine is the more potent S-isomer of the racemic drug, ketamine. Esketamine nasal spray used as an antidepressant has not been studied during breastfeeding. Minimal data indicate that single doses of intravenous esketamine or ketamine use during cesarean section delivery may not affect the breastfed infant or lactation. Until more data are available, repeated doses esketamine nasal spray should probably be avoided during breastfeeding. If esketamine is used, monitor the infant for sedation, poor feeding and poor weight gain.